This invention relates generally to the art of connecting data terminal equipment (DTE) users to remote computer systems (or hosts) through a wireless or radio wave data communication network. The invention disclosed may, however, be useful for other forms of data transmission and communication systems.
Over the past several decades, various communication networks have evolved to meet the growing need for access to information. Among the more familiar types of systems used for communication are wire-based telephone communication systems that use physical wires or optical fiber links to connect users. Data transmission using wire-based telephone communication systems can be accomplished using existing AT Modem technology. An AT Modem is a standard data communication equipment (DCE) connection device used with telephone equipment for converting or modulating an asynchronous stream of data into a phone line carrier signal. The connection between an AT Modem and a DTE, such as a personal computer or a portable computer, is usually through an RS-232 interface. One of the principal disadvantages of a wire-based telephone communication network is that users are limited to specific locations where wired connections are available. Another disadvantage is that wire-based telephone communication networks usually require dedicated telephone lines, which can be expensive.
Recently wireless data communication networks have emerged that enables information exchange by sending and receiving data through high frequency radio signals. Examples of such networks include the Mobitex Radio Network (Mobitex), which is operated by RAM Mobile Data, and Ardis, which is a joint venture of Motorola and IBM. Mobitex was developed in Sweden by Ericsson/Eritel and has been installed and is maintained in many other countries. For example, in Canada, Mobitex is operated by Roger's Cantel. Making efficient use of these wireless data communication networks to connect DTE users to remote computer systems is one of the objects of this invention.
Electronic data communication is organized into networks that have established protocols and specifications. Communication between computers takes place over a connection that is established using a common protocol. A data communication network generally refers to a collection or grouping of computers organized for co-operative communication of data. Once a connection is established, there are a number of data transfer methods used by various data communication networks. Both Mobitex and Ardis use packet switched data transfer methods, which aggregate data into blocks called packets before it is transmitted.
Ericsson also manufactures a device called a Mobidem, which is a radio based modem that is capable of transmitting digital information across the Mobitex data communication network. A Mobidem essentially provides an interface between a DTE user and Mobitex. Unfortunately, effective communication between a DTE user and a remote computer system across a wireless communication network, such as Mobitex, requires significant enhancements to support the standard AT Modem protocol. An object of this invention is to provide an enhanced user interface to a wireless data communication network such as Mobitex that is compatible with standard AT Modem technology.
A standard AT compatible modem is capable of sending a number of service signals to its DTE user that indicate changes in the status of the modem. For example, if the user makes a call to a remote computer system, several possible events may occur that result in associated service signals:
if the modem is disconnected, the message "No Carrier" will be displayed; PA1 if a connection is made, the message "Connect 2400" will be displayed; and PA1 if the call is made and the remote computer does not answer, "Busy" or "No Answer" will be displayed.
These messages can handle all of the events that can occur in the operation of a land-line modem (i.e. one that uses telephone lines).
The user of the modem has the option of setting various AT Modem parameters that affect whether service signals are transmitted by the modem to the DTE and the form in which they are transmitted. If the user enables the modem to transmit text service signals, the messages noted above will be transmitted to the DTE for display. If the user enables the modem to transmit numeric messages, the modem will transmit a numeric code to the DTE that corresponds to the event that occurred. If user does not enable the modem to transmit service signals, service signals will not be transmitted to the DTE.
Since any transmission from a remote computer to a DTE user through a wireless communication network such as Mobitex can be encoded with additional information, use of an AT compatible modem in conjunction with Mobitex adds a new dimension of information that can be displayed when an event occurs. An object of this invention is to enhance an AT compatible modem to transmit service signals that include information such as the identity of the caller and a presentation string.
All AT Modems have two basic states of operation; a command state and a data transfer state. In the command state, the DTE user can send command signals to the modem and change the modem's operating parameters. At start-up, an AT Modem is in the command state. When a connection is established, an AT Modem automatically shifts to the data transfer state. Because data received by a radio-based modem such as a Mobidem is received in packets, under certain conditions data will be waiting to be transmitted to the user immediately after the modem enters the data transfer state. Unfortunately, many DTE user applications will fail if the modem begins transmitting data to the user immediately after the modem transmits an entering-data-transfer-state signal. Another object of this invention is to provide a method for delaying data transmission by the modem to the user for a period of time after the modem has entered a data transfer state.